The overall objective of this project is to learn how alterations that occur in blood and tissue amino acid concentrations in response to alterations in the amino acid pattern and content of the diet influence food intake, food preferences and the metabolic fate of amino acids in brain, liver and muscle and in the intact animal. The immediate objectives are: 1) to investigate qualitatively and quantitatively, competition between amino acids that are present in excess in blood and the amino acid that is limiting for protein synthesis for entry into brain; 2) to examine the hypothesis that disproportionate amounts of some acids in blood, owing to dietary changes or metabolic defects in amino acid metabolism compete with the limiting amino acid for entry into brain and that depression of the uptake of the limiting amino acid initiates a signal leading to depression of food intake and alteration of food preference; 3) to determine the effects of changes in the amino acid pool of brain on brain protein synthesis and amino acid metabolism; 4) to investigate effects of nutritional modifications, especially changes in amino acid intake and dietary amino acid pattern, and hormonal treatments on amino acid transport into liver and muscle in an effort to assess the physiological significance of responses of transport systems in the regulation of metabolism of amino acids.